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Using Manufacturing Quality practices in PCB Design

What if you had a tool that could prevent problems in your processes and products before they occur?

Failure Mode and Effect Analysis (FMEA) is that tool. FMEA is a formal process of identifying all the ways a process or product can fail, and then determining how to reduce or eliminate them.

Product development groups and quality groups work tirelessly to identify ways their products and processes may fail. Identifying the ways products or processes may fail is the first step in either designing-in improvements, or taking steps to ensure those failures do not occur. There are several structured methodologies that can be used to work through defining potential failures and working through their effects. Failure Mode and Effect Analysis (FMEA) is one of these structured methodologies. It provides a way to examine the problem area, identify potential failures, identify the effects of those failures, and quantify those effects through various ranking values to come up with a priority rating that will allow teams to focus on the most critical potential failures, or failure modes. Although initially developed by the military, FMEA methodology is now extensively used in a variety of industries. The method is now supported by the American Society for Quality which provides detailed guides on applying the method.

There are several steps to using FMEA:

Scope of Study (Area to focus) – Defining the scope of a Failure Mode and Effect Analysis is very important. It must be well defined, with clear boundaries for the organization (management) and team members.

Identify Possible Failure Modes – The goal in this step is to identify all the ways things can go wrong. It is important not to get wrapped up around what that effects of the failure are…that comes next

Identify Possible Effects of Failure – Now that all the ways things can go wrong or may fail have been listed, each failure mode should be evaluated for the effects of the failure.

Define Severity Ranking – Severity ranking, as with Occurrence ranking and Detection ranking, are based on a 10-point scale, with one (1) being the lowest ranking and ten (10) being the highest ranking. Lower rank means a less severe failure mode. Typically in a Design FMEA, no effect would get a severity ranking of one, whereas noncompliance to regulatory requirements, or may cause harm to customers would be assigned a severity rank around 10.

Identify Occurrence Ranking – How often will a given failure mode occur?

Identify Cause of Failure – Brainstorming the cause of each failure should be done at this stage. Typically, subject matter experts, equipment vendors, vendor consultants, or outside consultants are used to fully analyze the causes of the failures.

Identify Detection Ranking – Detection ranking looks at how likely is it to detect a failure or the effect of a failure. Analysis of current controls to the product development flow should be done to determine the likelihood of detection.

Calculate Risk Priority Number – The Risk Priority Number defines the overall risk of a failure and its effect to the process or product. The Risk Priority Number (RPN) is calculated with a simple formula:

Risk Priority Number = Severity x Occurrence x Detection

The total risk priority number is calculated by adding the individual risk priority numbers of each failure and effect. Although this number in itself has no meaning, it is a way to gauge RPNs for a specific FMEA study as improvements are being made.

Prioritize Corrective Actions – The failure modes can now be prioritized by ranking them in order of the highest risk priority number to the lowest.

Now that we know how it works, how can we use it? One of the initial steps of an FMEA study is to identify possible “Failure Mode Causes”.

DFM Solutions as part of FMEA

Identifying ways products can fail in manufacturing is a tedious and often times trial and error process. Knowledge from years of previous product development and realization processes culminating in “out of the box” set of possible failure mode causes would dramatically improve identification of areas of risks, and effects of failures. Working through the FMEA processes outlined earlier, most DFM solutions come with analysis tools to identify potential design for manufacturability issues. As DFM manufacturing solutions are implemented, they can serve as both detection and control mechanisms for the FMEA process.

One of the most obvious examples is the potential failure mode caused by copper flooding under components with multiple ground connections, or similar condition. When assembly manufacturing PCBs which have passive components with uneven copper distribution between their leads, the differential in heat dissipation rates between the two leads may potentially cause cold solder joints and or slightly weaker solder adhesion, and thus leading to a potential tombstone problem.

In addition to aiding in identifying failure mode causes, DFM solutions may play a large part in providing control and managing the detection of the failures, before they happen. Detection should be managed with dual Design and Process control. This interrelationship between Design and Process should be maximized between Design FMEAs and process controls in place in manufacturing with parallel Process FMEAs in place.

I realize this is an overly simplified overview of a complex and comprehensive quality tool. However, I’m hoping the realization that good quality tools are out there, and design organization need not look any further than their manufacturing partners, vendors and suppliers alike for best practices and ways to identify and improve product quality.

Looking forward to any comments on the this topic, and FMEA’s applicability within the Design space.

Mentor Consulting provides customers with expertise in electronic design and manufacturing infrastructure and methodology. Valor Services include a worldwide team of professionals including former factory managers, engineering managers, software developers, designers and various experts who have improved PCB Assembly factories globally. Mentor Consulting solutions are engaged worldwide by forward-looking electronics companies to optimize design and manufacturing productivity and advance adoption of the latest industry best practices. For more information, contact mentor_consulting@mentor.com.

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Jay Gorajia is Worldwide Consulting Manager, PCB DFM and Manufacturing Solutions, for the Consulting Division of Mentor Graphics. He works to improve efficiency and help define productivity solutions in design, manufacturing engineering and production for OEMs and PCB Assembly manufacturers. Mr. Gorajia holds a Bachelor’s degree (B.Sc.) in Electronic Engineering and a Masters in Business Administration (MBA) in Technology Management. He has published a number of articles and White Papers in industry leading technical magazines and industry conferences.
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